When a moving site of the human body is scanned by an X-ray CT (Computed Tomography) apparatus, artifacts caused by motions occur in an acquired image. An X-ray CT apparatus generally scans an object from a plurality of projection angles in a circumferential direction to reconstruct a tomographic image using at least 180 degrees of projection data. Therefore, the above artifacts include at least 180 degrees of motion artifacts.
In order to reduce such motion artifacts, the method in which a motion amount and a motion speed of a site to be scanned are measured using a biosensor such as an electrocardiograph and a respiration sensor, a phase with the minimal motion amount is calculated, and an image is reconstructed by selecting projection data of the calculated phase has been proposed (Patent Literature 1).